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Abstract

Real-time imaging of gas leaks was demonstrated using an IR camera employing outdoor thermal background radiation. Ammonia, ethylene and methane detection was demonstrated in the spectral region 7–13 µm. Imaging was accomplished using an optical filter and a gascorrelation cell matching the absorption band of the gas. When two gases, such as ammonia and ethylene, are absorbing in the same wavelength region it is possible to isolate one for display by using gas-correlation multispectral imaging. Results from a field test on a leaking gas tanker are presented as QuickTime movies. A detection limit of 200 ppm×meter for ammonia was accomplished in this setup when the temperature difference between the background and the gas was 18 K and the frame rate was 15 Hz.

The normalized spectral response of the IR camera (dark blue curve) is convoluted with the transmittance of two different gas cell window materials and optical filter profiles, yielding two regions of relative response (black curves). The gases are both shown in absorbance at concentrations of 200 ppm×m.

A. Ammonia transmittance spectrum at a concentration of 400 ppm×m, convoluted with the system response. The black envelope integrated transmittance (no gas) divided by the integrated transmittance under the gas spectrum corresponds to the transmittance of the system. B. Ammonia transmittance spectrum at a concentration of 4000 ppm×m, convoluted with the system response.

Resulting calibrated ammonia gas concentration. Integrating the black envelopes in Fig. 3 corresponds to a transmittance value of one. Arrows A and B correspond to the integrated transmittance of the spectra in Fig. 3.

Theoretically calculated relative transmittance through 20000 ppm×m ammonia gas as a function of ΔT=TB-TG with TG=294 K. The results of an experimental verification are inserted with error bars in the figure.